Visual indicating spark plug with an integral gas lamp



R. w SMITH 3,343,087

VISUAL INDIGATING SPARK PLUG WITH AN INTEGRAL GAS LAMP Oct. 17, 1967 2 Sheets-Sheet 1 Filed April 12, 1965 A T TORNE Y 2 Sheets-Sheet 2 Z 0 r a W w W Z 4 5 WM WM Oct. 17, 1967 w, sMlTH VISUAL INDICATING SPARK PLUG WITH AN INTEGRAL GAS LAMP Filed April 12, 1965 h HH, w M ww W W n i m 6 U ADI I 7w w United States Patent 3,348,087 VISUAL INDICATING SPARK PLUG. WITH AN INTEGRAL GAS LAlVIP Robert W. Smith, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Apr. 12,- 1965, Ser.,No. 447,318 9 Claims. (Cl. 3131) This invention relates to spark plugs and to a method for making same. More particularly, it relates to a spark plug which functions as a visual indicator for the sparking operation of the'spark-plug;

The conventionalway'of checking the operation of a spark plug is by disconnecting the high tension cable from the spark plug and causing a spark between the cable and the cylinder block by cranking the motor. Many attempts have been made to replace this cumbersome test with an easier, quicker visual test means. These visual indicators have taken many forms. One such indicator is described in US. Patent 1,690,702 in which a visual test unit is built onto the top of a standard spark plug insulator. The expense and technical dificulties encountered with such a plug prohibits its commercial use toany extent. Another type of indicator used'to some extent for detecting spark plug operation is the pencil-like neon bulb unit which is electrically connected with the spark plug electrodes as disclosed in US. Patent 1,957,802. The sparking operation can be viewed through a window in these pencil-like units. The disadvantages of these pencil-like testers which have limited its wide use are theinconveniences of carrying about an auxiliary test device and the necessity of having to locate the viewing window in the line of sight of the observer. A difierent approach to this problem is discussed in copending Ser. No. 217,086, filed Aug. 15, 1962, now Patent No. 3,242,366 and assigned to the assignee of this invention, in which a neon bulb is inserted into a spark plug insulator body, the insulator body having translucent portions thereof topermit the visual observation of the sparking operation. Such a spark plug having a neon bulb inserted within the insulator body performs satisfactorily and is very convenient; however, the high cost of such a spark plug has limited commercial use.

It is the basic object of this invention to provide a spark plug having visual means to indicate sparking performance. When a sparking voltage is applied to the spark plug, the energized inert gas in the insulator body chamber glows through the annular translucent insulator walls, thereby indicating to an observer the presence of high voltage at the spark plug. It is another object of this invention to provide a method by which a visual indicating spark plugmay be manufactured. v

These and other objects are accomplished by a method of manufacturing a spark plug comprising the steps of inserting a center wire into the centerboreof a spark plug insulator body having annular translucent portions thereon, loading and packing a layer of metal-glass powder which covers the center wire head, loading and packing a layer of metal powder which serves as one of the insulator body chamber electrodes on top ofthe metal-glass powder layer. Thereafter, a metal tube having a lower portion of enlarged diameter that is flanged outwardly is placed so that the flanged portion rests upona shoulder in the upper portion of the insulator centerbore; This tube serves as the other insulator body chamber electrode and as a vent. A layer of glass powder is loaded and packed on top of the flanged lower portion of the tube, between the insulator walls and the middle portion of the tube. The glass powder and the metal-glass powder are melted at elevated temperatures and thencooled to form hermetic seals. The chamber formed between the two seals in the 3,348,037 Patented Oct. 17, 1967 Ice insulator body centerbore is then evacuated through the tube and then back-filled with an inert gas. When the proper inert gas pressure is obtained, the vent is sealed. The terminal is then fastened to the top of the insulator body and the standard spark plug shell is placed around the insulator body and fastened.

Other objects andadvantages of this invention will be apparent from the following detailed description, reference being made to the accompanying drawings wherein a preferred embodiment of this invention is shown.

In the drawings:

FIGURE 1 is a longitudinal cross-sectional view of the visual indicating spark plug of this invention; 7

FIGURE 2 is a longitudinal cross-sectional view of the lower portion of the insulator body;

FIGURES 3, 4, 5 and 6 are longitudinal cross-sectional views of the upper portion of the insulator body at different stages in the manufacturing process.

Referring to FIGURE 1 of the drawings, the spark plug 10 comprises a conventional outer metal shell 12 having a ground electrode 14 welded to the lower end thereof.

Positioned within the metal shell 12 and secured in the conventional manner is an insulator 16. The insulator is preferably of a'ceramic material composed of at least alumina and is of the type fully described in US. Patent 2,760,875, issued to Karl Schwartzwalder and Helen Blair Barlett. Such an insulator has excellent mechanical strength, heat shock resistance and translucency properties, all of these characteristics being of considerable advantage in forming the visual indicating spark plug of this invention. The insulator 16 is formed with a centerbore having a lower portion 18 of relatively small diameter, a lower center portion 20 of larger diameter, an upper center portion 22 of still larger diameter, and an upper portion 23 of yet still larger diameter. Near the top of the upper. center portion 22 the insulator has zones of relatively thin cross sections as shown by annular rings 24 The translucent zones formed by these annular rings 24 in the walls of the insulator 16 permit light from within the insulator core to be visible uniformly around the insulator to an observer from without. For example, an observer looking at insulator 16 during the operation of the spark plug would see a high frequency flutter or glow at the annular depressions or rings 24. Such a glow would naturally be more apparent during hours of darkness. However, the preferred embodiment of this invention as illustrated compensates for the loss in contrast during hours of daylight by providing for shadow casting projections or shoulders 26 which increase the illumination effect at the glow rings 24. The configuration of the annular depressions 24 and shoulders 26 is disclosed in the aforementioned copending Ser. No. 217,086 and has been found to function satisfactorily.

Positioned in the lower portion 18 of the insulator centerbore is the center electrode 28, the serrated lower end thereof projecting beyond the lower tip of the insulator 16. The center electrode head 30 rests on insulator centerbore ledge 32, the insulator centerbore ledge 32 connecting the lower center portion 20 to the lower portion 18 of the insulator centerbore. A metal-glass seal 34 as will be hereafter fully described forms a hermetic seal between the center electrode head 30 and the insulator centerbore wall of the lower center portion 20. On top of the metal-glass seal 34 is a layer of metal powder 36 which serves the lower electrode in the insulator body chamber. The lower electrode 36 may be any conductive metal such as copper, nickel, iron, platinum, silver, tungsten, and Kovar with Kovar powder being used in the preferred embodiment. Above the lower electrode 36 is a sealed insulator body chamber 38 which extends up to the electrode and exhaust stem assembly 40. The insulator body chamber 38 con- .3 tains an inert gas, which is neon in the preferred embodiment. The electrode and exhaust stern assembly 40 consists of a metal tube as will be hereafter fully described whose lowerportion extends outwardly in a conical fashion similar to a funnel so that the lower flanged end of the tube has a diameter similar to the diameter of the insulator centerbore at the position of the ledge 41. The

flanged end of the electrode and exhaust stem assembly U 40 is positioned on top of the insulator centerbore ledge 41, ledge 41 connecting the upper center portion 22 with the upper portion 23 of the insulator centerbore. The upper end of the electrode and exhaust stem assembly 40 is Welded shut thereby making that end of the assembly 40 air tight. Glass'seal 42 forms a hermetic seal between the I upper surface of the lower portion of the electrode and exhaust stern assembly 40 and the insulator centerbore wall of the upper portion 23.

The terminal 44 encloses and covers the upper portion of the electrode and exhaust stem assembly 40 and fits over the top end of the insulator body 16. The lower end of the terminal 44 is crimped over the insulator body under rib 43 thereby locking the two elements tightly together. The terminal 44 may be in electrical contact with the electrode and exhaust stemassembly 40, in which case, the current is conducted through the electrical contact. However, if the terminal 44 is not in electrical contact with the electrode and exhaust stem assembly 40 the current jumps the gap between the terminal 44 and the electrode and exhaust stem assembly 40. The terminal 44 just described was the one piece terminal head; however, the two piece terminal in which a cap screws over a screw top may be used in this invention as well.

During the sparking operation of the visual indicating spark plug described in FIGURE 1, the current passes from the spark plug terminal 44 to the electrode and the exhaust stem assembly 40. As the currenttraverses the chamber 38 separating the electrode and exhaust stem assembly 40 from the metal electrode 36, the inert gas is energized, thereby resulting in a glowing. insulator body. which projects light through the translucent insulator wall 24 to indicate to an observer the presence of a high voltage in the spark plug. The current then passes from the metal electrode 36 in the conventional way through the metal seal 34, through the center wire electrode 28, across the gap to the side electrode 14, and then to the shell 12 where it is grounded to the engine block (not shown). I

Referring now to FIGURES 2 through 6, thisinvention willnow be described in greater detail in terms of a method for making a visual indicating spark plug. As shown in FIGUREZ, the center wire electrode 28 is inserted into the centerbore of an insulator body 16.7The center wire electrode head 30 rests upon the insulator ledge 32. A

metal-glass seal powder load 34 ranging from 0.25 to 0.35

gram is placed on top of the center wire head 30 in the centerbore portion 20 in the conventional manner and tamped. The composition of this metal-glass powder 34 is an important aspect because this metal-glass powder must form a hermetic seal without being pressed by a terminal screw or other means as in the usual practice; therefore, this seal, upon heating alone, must be of such a composition that it will form a hermetic seal. The composition of such a metal-glass powder is the subject of the co-pending patent application A-377Q filed simultaneously with this application and assigned to the assignee of this invention. An essential component of this metal-glass powder 34 isthe metal. The coefficient of expansion for the metal must be similar to glass thereby permitting the glass and the metal of this metal-glass mixturetoexpand upon heating and contract upon cooling at the same rate. The fused .glass and metal contract upon cooling at the same rate to form a hermetic seal. Kovar metal alloy is 'used in the preferred embodiment. Kovaris a low expansion, iron based alloy with 28 to 30% of nickel and 15 to 18% cobalt and fractional percentages of manganese.

4 Other metals having a coeflicient of expansion similar to glass which may be used are molybdenum and tungsten. The mesh size of the metal powder in this metal-glass powder mixture is important to obtain a conductive seal. There must be at least 35 weight percent of the metalparticles having a size larger than 100 mesh to insure electrical conductivity in the fused metal-glass seal. The Kovar powder used in the preferred embodiment had 36 weight percent particles which passed through a minus 35 to 100 mesh screen sieve.

A metal-glass powder mixturewhich worked well is as follows:

Parts by weight Coming 7052 Glass or equivalent (Kimball) 38 Boric anhydride 2 Kovar powder Hydrogenatedcottonseed oil' 3 The Corning 7052 glass is a glass powder frequently used for spark plug glass seals. The composition of this glass is SiO 23% B 0 5% A1 0 and 7% Na O. The amount of glass powder in the metal-glass powder 7 mixture 34 ranges from 30 to 45%. The mesh size of,

ranges from 1 to 4%. Hydrogenated cottonseed oil is a binder frequently used for spark plug glass seals which burns ofi during the scaling 'to prevent oxidation of the metal. The amount of binder, hydrogenated cottonseed oil in the preferr'ed embodiment, in the metal-glass mix- 'ture ranges from 1 to 3%. Asindicated earlier, in the preferred embodiment, the Kovar metal powder is an es.- sential component in thismetal-glass .seal composition. The amount of Kovar powder in the metal-glass powder mixture 34 ranges from 55 to the lower figure in-.

dicating the minimum amount of metal required to adequately conduct the electrical current and the higher figure making provision for the minimum amountof glass needed for fluidity and sealing purposes. A layer of 0.10

to 0.2.0 gram of Kovar powder 36 is placed on top of the metal-glass seal 34 and tamped. This Kovar powder layer forms the lower electrode 36 in the insulator body chamber 38. Other metal powders, such as iron, nickel, and so forth, may be used for this electrode.

As shown in FIGURE 3, the "electrode and exhaust assembly 40 is inserted into the insulator 'ce'nterbore so that it rests upon ledge 41. As described earlier, the assembly 40 consists of a metal tube whose lower portion extends outwardly in a conical fashion similar to a funnel. It is the flanged lower end of assembly 40 that rests npon'the insulator ledge 41. In the preferred embodiment, this assembly is made out of Kovar. Other metals Qor metal a1- loys which have a coeflicient of expansion which is similar to glass such'as molybdenum and tungsten may be used. Although FIGURE 3 discloses a metal tube as the electrode and exhaust assembly '40, this invention is not limited to the use of such a tube. The area immediately above and surrounding the electrode and exhaust stern assembly 40 is filled with 0.20 'to 0.30 gram of a 'glass seal 42 powder such as Corning 7052 glass powder or an equivalent. The insulator is then heated in air at approximately 1740 F for 10 minutes 'in order to melt the glass powder 42 and the metal-glass powder mixture 34, thereby forming the hermetic insulator bodychamber 38 (see FIGURE 1). Since the lower flanged end of the electrode and exhaust stem assembly 40'does not form a hermetic seal with the insulator body 16 when it is positioned on hauststem assembly 40 and the insulator center'bore wall of the upper portion 24 after it is heated. In order to do i this, it is essential that the electrode and exhaust stem assembly 40 which comes in contact with the glass seal be made of Kovar or another metal which has expansion characteristics that are similar to glass. Since the glass 42 and the Kovar electrode and exhaust stem assembly 40 have similar coefl'icients of expansion, a hermetic seal is formed. If a metal is used having a coeflicient of expansion different than glass, temperature changes would cause the glass 42 to separate or break away from the electrode and exhaust stem assembly 40. This results in a leaky seal which in turn causes malfunctioning in the insulator body chamber 38.

As shown in FIGURE 4, the upper end 39 of the electrode and exhaust stem assembly 40 is connected with tubing 46 to a valve 48 which is in communication with a vacuum pump 50 and an inert gas supply 52. With the valve 48 open to vacuum pump 50, the vacuum pump is used to evacuate the insulator body chamber 38. When the air has been removed from the insulator body chamber 38, the valve is turned so that the inert gas supply 52 is in communication with the insulator body chamber 38. Although the chamber may be filled with any inert gas, neon gas or a helium-neon gas mixture is preferred. When neon gas or a helium-neon gas mixture is used, the preferred pressure in the insulator body chamber 38 is between and 30 centimeters of mercury. The pressure in chamber 38 is obtained and measured by a pressure gauge (not shown) connected to the inert gas supply 52. Pressures lower than 10 centimeters of mercury cause overheating, variations in gas pressure, and an uneven distribution of current throughout the chamber. Gas pressures higher than 30 centimeters of mercury tend to be uneconomical. Excessively high pressures cause the light in the chamber 38 to be uneven, to waiver and to show threads of light. For inert gases other than neon or a helium-neon mixture, the desired pressure range may be diiferent. When the neon gas or other inert gas in the chamber 38 is at the proper pressure, the upper end 39 of the exhaust stem 40 is pinched and welded to form an air-tight seal 45 as shown in FIGURE 5. The lower end of the terminal 44 has a central opening therein thereby permitting the terminal 44 to fit over the sealed exhaust stem 45 and having the lower annular terminal edge 48 protruding below the insulator body rib 43 so that the annular terminal edge 48 can be mechanically crimped under the rib 43. The insulator body assembly thus formed is inserted into a conventional spark plug shell 12 as shown in FIGURE 1 in the conventional manner to form a visual indicating spark plug.

While the invention has been described in terms of a specific embodiment, it is to be understood that the scope of the invention is not limited thereby except as defined in the following claims.

I claim:

1. A spark plug having means which serve as a visual indicator during sparking operations comprising an insulator having a centerbore therethrough and having translucent wall portions thereof, a terminal positioned above said insulator, a center electrode positioned in the lower portion of said centerbore, two hermetically sealed electrodes in spaced relationship in said centerbore, said two hermetically sealed electrodes and insulator walls forming a chamber in said centerbore, said insulator translucent wall portions forming a portion of sa d chamber, said chamber containing an inert gas, one of said sealed electrodes connected with said terminal and the other said sealed electrode connected with said center electrode.

2. A spark plug having means which serve as a visual indicator during sparking operations comprising an in sulator having a centerbore therethrough and having translucent wall portions thereof, two hermetically sealed electrodes in spaced relationship in said centerbore, said two electrodes and insulator walls forming a chamber in said centerbore, said insulator translucent wall portions forming a portion of said chamber, said chamber containing an inert gas, means electrically connected to said two electrodes whereby a voltage applied to said spark plug suflicient to produce a spark with said spark plug simultaneously energizes said inert gas between said two electrodes in said chamber sending visible light through said translucent wall portions to indicate spark plug operation.

3. A spark plug having means which serve as a visual indicator during sparking operations comprising an insulator having a stepped centerbore therethrough providing an upper and lower ledge therein and having wall portions sufficiently thin to be translucent, a hermetically sealed lower electrode in the form of a compacted layer of metal powder in the lower portion of said centerbore, a hermetically sealed upper electrode in the form of a flanged metal tube in the upper portion of said centerbore, said upper electrode having the flanged end thereof positioned on the upper ledge in said centerbore, said upper electrode being in spaced relationship with said. lower electrode in said centerbore, said hermetically sealed upper and lower electrode and insulator walls forming a chamber in said centerbore, said insulator translucent wall portions forming a portion of said chamber, said chamber con taining an inert gas, means electrically connected to said upper electrode and said lower electrode whereby a voltage applied to said spark plug sufficient to produce a spark with said spark plug simultaneously energizes said inert gas between said lower electrode and said upper electrode in said centerbore chamber sending visible light through said translucent wall portions to indicate spark plug operation.

4. A spark plug described in claim 3 wherein said upper electrode is made of a metal taken from the group consisting of Kovar, molybdenum, and tungsten.

5. A spark plug described in claim 3 wherein said inert gas is neon gas.

6. A spark plug as described'in claim 3 wherein said chamber has an inert gas pressure ranging from 10 to 30 centimeters of mercury.

7. A spark plug having means which serve as a visual indicator during sparking operations comprising a metal shell having a side electrode secured to the lower end thereof, an insulator mounted concentrically within said shell and having a stepped centerbore therethrough providing an upper and lower ledge therein, said insulator body formed of a ceramic material comprising at least alumina and having wall portions sufiiciently thin to be translucent, a metal center electrode having a head portion formed at the upper end thereof which is positioned on the lower ledge in said centerbore, said center electrode having a lower portion protruding out of said insulator centerbore whereby the tip of said lower portion is spaced in spark relation to said side electrode, a conductive fused layer of a mixture of glass and metal powder in said centerbore above and bonded to said head portion of said center electrode whereby the center electrode is hermetically sealed with said insulator, a lower electrode in the form of a compacted layer of metal powder in said centerbore above and in contact with said conductive fused metal-glass layer, an upper electrode in the form of a flanged metal tube in the upper portion of said centerbore having the flanged end thereof positioned on the upper ledge in said centerbore and being in spaced relationship with said lower electrode, a fused layer of glass powder in said centerbore above and bonded to the flanged portion of said upper electrode whereby the said upper electrode is hermetically sealed with said insulator, said hermetically sealed upper and lower electrodes and insulator walls forming a chamber in said centerbore, said insulator translucent wall portions forming a portion of said chamber, said chamber containing an inert gas, a terminal being in electrical connection with said upper electrode and positioned on top of said insulator whereby the lower annular edge thereof is secured about the upper portion of said insulator whereby a voltage applied across the sparking gap separating the side electrode from the center electrode sufiicient to produce a spark therebetween simultaneously energizes said inert gas between said upper electrode and said lower electrode in said chamber, sending visible light through said translucent wall portions to indicate spark plug operation.

8. A spark plug having means which serve as a visual indicator during sparking operations comprising a metal shell having a side electrode secured to the lower end thereof, an insulator mounted concentrically within said shell and having a stepped centerbore therethrough providing an upper and lower ledge therein, said insulator body formed of a ceramic material comprising at least 85% alumina and having wall portions sufiiciently thin to be translucent, a metal center electrode having a head portion formed at the upper end thereof which is positioned on the lower ledge in said centerbore, said center electrode having a lower portion protruding out of said insulator centerbore whereby the tip of said lower portion is spaced in spark relation to said side electrode, a conductive fused layer of a mixture of glass and metal powder in said centerbore above and bonded to said head portion of said center electrode whereby the center electrode is hermetically sealed with said insulator, said metalglass fused layer containing a metal taken from the group consisting of Kovar, tungsten and molybdenum; a lower electrode in the form of a compacted layer of metal powder in said centerbore above and in contact with said conductive fused metal-glass layer, an upper electrode in the form of a flanged metal tube in the upper portion of said centerbore having the flanged end thereof positioned on the upper ledge in said centerbore and being in spaced relationship with said lower electrode, a fused layer of glass powder in said centerbore above and bonded upper electrode is hermetically sealed with said insulator, said hermetically seale'dupperand lower electrodes and insulator walls forming a chamber in said centerbore, said insulator translucent wall portions forming a ortion of said chamber, said chamber containing an inert gas, a terminal being in electrical connection with said upper electrode and positioned on top of said insulator whereby the lower annular edge thereof is secured about the upper portion of said insulator whereby a voltage applied across the sparking gap separating the side electrode from the center electrode sufficient to produce a spark therebetween simultaneously energizes said inert gas between said upper electrode and said lower electrodein said chamber sending visible light through said translucent wall portions to indicate spark plug operation.

9. A spark plug as described in claim 8 wherein said fused metal-glass layer contains at least weight percent of the metal particles having a size larger than mesh.

References Cited UNITED STATES PATENTS 1,548,031 8/1925 ranzen 313- 429 X 1,690,702 11/1928 Rotella 3l3-12O X 1,957,802 5/1934 Rebezzana 324-17 2,479,821 5/1949 Humrichouse et al. 313-124 X 3,242,366 3/1966 Candelise et al. 313-123 X JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

1. A SPARK PLUG HAVING MEANS WHICH SERVE AS A VISUAL INDICATOR DURING SPARKING OPERATIONS COMPRISING AN INSULATOR HAVING A CENTERBORE THERETHROUGH AND HAVING TRANSLUCENT WALL PORTIONS THEREOF, A TERMINAL POSITIONED ABOVE SAID INSULATOR, A CENTER ELECTRODE POSITIONED IN THE LOWER PORTION OF SAID CENTERBORE, TWO HERMETICALLY SEALED ELECTRODES IN SPACED RELATIONSHIP IN SAID CENTERBORE, SAID TWO HERMETICALLY SEALED ELECTRODES AND INSULATOR WALLS FORMING A CHAMBER IN SAID CENTERBORE, SAID INSULATOR TRANSLUCENT WALL PORTIONS FORMING A PORTION OF SAID CHAMBER, SAID CHAMBER CONTAINING AN INERT GAS, ONE OF SAID SEALED ELECTRODES CONNECTED WITH SAID TERMINAL AND THE OTHER SAID SEALED ELECTRODE CONNECTED WITH SAID CENTER ELECTRODE. 